Presently, most semiconductor devices are sealed or encapsulated with an epoxy resin based plastic molding encapsulant. The dramatic increase in the memory capacity of these semiconductor devices has greatly increased the degree of integration and are moving toward larger chip size and finer circuitry. The larger chip size and finer circuits have made these micro devices more susceptible to failure due to internal stress believed to be produced by the shrinkage during the cooling process from curing temperature to room temperature. This thermal stress is believed to be the primary cause for such failures as package crack, passivation film crack, wire deformation and delamination of the encapsulated micro devices during temperature fluctuations.
Present electronic grade epoxy resin based molding formulations do not possess the physical properties required to withstand the vigorous thermal environment the integrated circuit devices will experience during actual usage. Formulators are presently blending commercially available elastomeric additives into their molding or encapsulating formulations in order to increase toughness so as to enable the encapsulated device to withstand thermal shock, i.e. cycling from cold to hot temperatures. However, only a marginal increase in toughness with a decrease in the glass transition (Tg) temperature is obtained by this additive method.
It would therefore be desirable to have available an epoxy resin base which would enable the resultant encapsulated or molded electrical or electronic devices to possess increased toughness, thermal shock resistance with a minimal loss in the glass transition temperature.